1. Field Of The Invention
This invention relates to baffles positioned in well casing and used for such operations as fracturing and treating, and more particularly, to a baffle which may be set on a wireline. In some embodiments, the baffle is retrievable.
2. Description Of The Prior Art
In multiple stage fracturing jobs in oil and gas wells, one or more tubing or casing baffles are positioned in the completion string between the well zones which are to be stimulated. Proper placement of the fracturing baffles in the production casing permits accurate control of fluid entry into the zone or zones to be fractured.
Each zone may be perforated, fractured and then temporarily isolated with a bridging ball while a more shallow zone is being completed in a similar manner. Thus, a multiple stage fracturing operation usually can be completed in a semi-continuous manner allowing for the short time delay required to perforate each zone before treatment.
Such casing baffles, which have been in wide use for a number of years, are installed as the casing is made up and run into the hole. The baffles have graduated internal openings, and sealing balls or free-fall plugs are selected and mated with the baffles so that the smaller diameter balls or plugs will pass through the larger baffles that are installed at the more shallow depths. The balls and plugs are of such density that they usually are expelled from the tubing with the flow of fluids and gas when the well is opened to test or production.
When this method is used, pin-point stage fracturing of massive oil or gas production zones usually can be achieved rapidly and economically with less time required than when using bridge plugs, straddle packers, and other conventional tools for multiple zone isolation.
As mentioned, these previously known baffles require placement of the baffle in the casing while the casing string is assembled and run into the well bore. This obviously requires preplanning. In addition, the baffles in the casing may limit the use of perforation isolation packers, such as the Halliburton pin point injection packer. Another problem is that some operations do not have the drilling supervision necessary to insure the baffle is placed at the required point in the casing string. Such supervision usually requires a geologist who can pick the point in the open hole and a drilling foreman to insure the baffle is placed between the correct casing joints. In some cases, there is a relatively small distance between zones, and if the casing tally or driller's total depth measurement is off, the baffles may be placed in such a position that other multiple stage fracturing methods have to be employed. Errors of one hundred feet are not uncommon in pipe tally or driller's total depth measurements, and there are known zones in which the depth between zones is only forty to sixty feet.
The wireline set baffle of the present invention may be positioned in the casing string above a fracture interval after the casing is already in the well bore. It is not necessary to install the present baffle beforehand. The baffle of the present invention may be run on an electric wireline, slick-line, sand-line, tubing or coiled tubing. With any of these techniques, the baffle may be accurately placed and no preplanning of its placement prior to cementing is required.
Another problem with prior art baffles is that they become a permanent portion of the casing string and may not be retrieved. In the present invention, some of the embodiments of the baffle are retrievable.